Selective hydrogenation process employing a catalyst having a controlled porosity

ABSTRACT

A process for jointly carrying out selective hydrogenation of polyunsaturated compounds into monounsaturated compounds contained in gasolines, and for transforming light sulphur-containing compounds into heavier compounds by reaction with unsaturated compounds employing a supported catalyst, comprising at least one metal from group VIB and at least one non-noble metal from group VIII used in the sulphurized form deposited on a support and having a controlled porosity, and comprising bringing the feed into contact with the catalyst at a temperature in the range of 80° C. to 220° C. at a liquid hourly space velocity in the range of 1 h−1 to 10 h−1 and at a pressure in the range of 0.5 to 5 MPa.

FIELD OF THE INVENTION

The production of gasoline satisfying new environmental specificationsrequires a large reduction in their sulphur content to values whichgenerally do not exceed 50 ppm and are preferably less than 10 ppm.

It is also known that conversion gasolines, more particularly those fromcatalytic cracking, which may represent 30% to 50% of the gasoline pool,have high mono-olefin and sulphur contents.

Thus, almost 90% of the sulphur present in the gasoline can beattributed to gasolines from catalytic cracking processes, hereinaftertermed FCC gasoline (fluid catalytic cracking). FCC gasolines thusconstitute the preferred feed for the process of the present invention.

More generally, the process of the invention is applicable to anygasoline cut containing a certain proportion of diolefins and which mayalso contain several lighter compounds from C3 and C4 cuts.

Gasolines from cracking units are generally rich in mono-olefins andsulphur, but also in diolefins in an amount, for gasolines fromcatalytic cracking, of 1% by weight to 5% by weight. Diolefins areunstable compounds which polymerize easily and must generally beeliminated before processing those gasolines, such as by usinghydrodesulphurization treatments intended to satisfy specificationsregarding the amount of sulphur in gasolines. However, thathydrogenation must be selectively applied to diolefins to limit thehydrogenation of mono-olefins and to limit the consumption of hydrogenand the octane loss of the gasoline. Further, as described in EP-A1-1077 247, it is advantageous to transform saturated lightsulphur-containing compounds, which are sulphur-containing compoundswith a boiling point lower than that of thiophene, such as methanethiol,ethanethiol or dimethylsulphide, into heavier compounds before thedesulphurization step, as that can produce a desulphurized gasolinefraction mainly composed of mono-olefins containing 5 carbon atomswithout a loss of octane by simple distillation. The sulfur content inthe feedstock after selective hydrogenation and the transformation oflight sulphur-containing compounds into heavier compounds is notmodified, only the nature of the sulfur is modified due to thetransformation of light sulphur-containing compounds into heaviercompounds.

Further, the diene compounds present in the feed to be treated areunstable and tend to form gums by polymerizing. Such gum formationcauses progressive deactivation of the selective hydrogenation catalystor progressive plugging of the reactor. For industrial application, itis thus important to use catalysts which limit the formation ofpolymers, i.e. catalysts having a low acidity or wherein the porosity isoptimized to facilitate continuous extraction of polymers or gumprecursors by the hydrocarbons of the feed, to ensure a maximum lifecycle for the catalyst.

The present invention pertains to the use of a novel catalyst in aprocess that can jointly carry out hydrogenation of polyunsaturatedcompounds, and more particularly of diolefins, and transform lightsulphur-containing compounds, more particularly mercaptans, into heaviercompounds.

One advantage of the invention is to facilitate sulphur elimination bytransforming mercaptans into heavier compounds to separate them moreeasily and thus eliminate them in a subsequent hydrodesulphurizationstep.

Another advantage of the invention is to produce a gasoline having ahigh octane index.

A further advantage of the invention is to eliminate diolefin compoundsand thus to stabilize the feed before its passage into thehydrodesulphurization unit.

A third advantage of the invention resides in the fact that the catalystformulation is adjusted to ensure better stability of the catalyst asregards polymer formation, good selectivity as regards diolefinhydrogenation and good activity in the conversion of mercaptans andother light sulphur-containing compounds.

PRIOR ART

The literature describes catalytic formulations or processes which caneither selectively hydrogenate diolefins to mono-olefins or transformmercaptans by transforming them into heavier compounds, or carry outthese two types of reaction in one or two steps.

The use of catalysts containing at least one noble metal is known. Manypatents propose catalysts for selective hydrogenation which containpalladium. Palladium is known for its hydrogenating activity and iswidely used in selective hydrogenation processes. However, palladium issensitive to poisons and in particular to the presence of sulphur. Thepresent invention differs from those catalysts in that the catalyst ofthe invention contains no palladium and, more broadly, contains no noblemetals.

European patent application EP-A1-0 685 552 proposes a process forhydrogenating diolefins and reducing the mercaptans content of acatalytically cracked gasoline based on a catalyst containing between 0.1% and 1% by weight of palladium.

European patent application EP-A1-0 623 387 proposes a catalystcomprising at least one group VIII metal preferably selected fromplatinum, palladium and nickel and at least one additional metal Mpreferably selected from the group formed by germanium, tin, lead,titanium, iron, molybdenum, tungsten and rhenium. The catalyst ischaracterized in that the group VIII metal is activated by reduction inthe reactor before introducing the metal M. The catalyst of the presentinvention differs from that patent in that it does not undergo reductionduring the preparation phase.

The following patents and patent applications propose solutions forselectively hydrogenating diolefins; reactions which may affectsulphur-containing compounds, if they are present, are not mentioned.

U.S. Pat. No. 6,469,223 concerns a process for selective hydrogenationof diolefins on a catalyst containing nickel and molybdenum on analumina-based support. The process is characterized in that the nickeland molybdenum metals are used in the form of oxides. The presentinvention differs from that prior art in that the metals are used in theform of metal sulphides rather than oxides.

U.S. Pat. No. 3,472,763 proposes a process for selective hydrogenationinvolving a nickel-based catalyst supported on alumina. The catalyst mayalso, and preferably, contain between 1% and 10% of molybdenum. Thatcatalyst is also characterized by a pore distribution such that thetotal pore volume is more than 0.4 cm³/g, with 40% to 80% of that volumecorresponding to pores with a diameter of more than 0.05 and whereinpores with a diameter in the range 0.05 to 1 micron represent more than20% of the pore volume. That patent also teaches that it is preferableto reduce the metals before their partial sulphurization. The catalystof the present invention differs from that prior art primarily in theamount of molybdenum, which is over 10% by weight, and by thesulphurization step which is carried out on the metals in the oxidestate.

The following patents and patent applications propose solutions totransform mercaptans into heavier compounds by thioetherificationreactions, and optionally to selectively hydrogenate diolefins.

U.S. Pat. No. 5,807,477 proposes a process which, in a first step, cantransform mercaptans into sulphides by addition to diolefins on acatalyst comprising a group VIII metal, preferably nickel, in the oxideform, then in a second step, selectively hydrogenating the diolefins ina reactive distillation column in the presence of hydrogen. The presentinvention differs from that patent in that the selective hydrogenationand steps for transforming the sulphur-containing compounds into heaviercompounds are carried out jointly on the same catalyst used in thesulphurized form.

U.S. Pat. No. 5,851,383 describes a process for selective hydrogenationand thioetherification of C3-C5 cuts characterized by a distillationapparatus comprising two fractionation zones which can separatelyrecover the light compounds and the thioethers. The catalysts describedare either catalysts based on a group VIII metal or resins containing ametal. A catalyst containing between 15% and 35% of nickel is preferred.The catalyst of the present invention differs from the catalyst in thatpatent as the hydrogenation metal is a group VIB metal and the nickelcontent is less than 15% by weight.

In the light of the solutions described in the literature, the presentinvention proposes a process which can jointly carry out hydrogenationof polyunsaturated compounds, more particularly diolefins, and transformlight sulphur-containing compounds, more particularly mercaptans, intoheavier compounds using a catalyst with a controlled porosity. Saidcatalyst has improved stability and activity compared with prior artcatalysts.

BRIEF DESCRIPTION OF THE INVENTION

The present invention describes a process for selective hydrogenation ofpolyunsaturated compounds, more particularly diolefins, which canjointly transform saturated light sulphur-containing compounds, moreparticularly mercaptans, into heavier compounds, said process employinga catalyst containing at least one metal from group VIB and at least onenon-noble metal from group VIII deposited on a porous support, in which:

-   -   the amount, by weight of oxide, of the group VIB element is        strictly greater than 12% by weight;    -   the amount, by weight of oxide, of the group VIII element is        less than 15% by weight;    -   the degree of sulphurization of the constituent metals of said        catalyst is at least 60%;    -   the volume of pores with a diameter of more than 0.05 microns is        in the range 10% to 40% of the total pore volume.

The process consists of passing a mixture, constituted by the gasolineto be treated and hydrogen, over the catalyst.

The hydrogen is generally introduced in a slight excess, up to 5 molesper mole, with respect to the stoichiometry necessary to hydrogenate thediolefins (one mole of hydrogen per mole of diolefin).

The mixture constituted by gasoline and hydrogen is brought into contactwith the catalyst at a pressure in the range 0.5 to 5 MPa, a temperaturein the range 80° C. to 220° C., with a liquid hourly space velocity(LHSV) in the range 1 h⁻¹ to 10 h⁻¹, the liquid hourly space velocitybeing expressed in liters of feed per liter of catalyst per hour(1/l/h).

DETAILED DESCRIPTION OF THE INVENTION

The invention concerns a process for the treatment of gasolinescomprising any type of chemical family, in particular diolefins,mono-olefins and sulphur-containing compounds in the form of mercaptansand light sulphides. The present invention is of particular applicationin the transformation of conversion gasolines, in particular gasolinesfrom catalytic cracking, fluidized bed catalytic cracking (FCC), acokefaction process, a visbreaking process, or a pyrolysis process.Feeds to which the invention is applicable have a boiling point in therange 0° C. to 280° C., more precisely between 30° C. and 250° C. Thefeeds may also comprise hydrocarbons containing 3 or 4 carbon atoms.

As an example, gasolines from catalytic cracking units (FCC) contain, onaverage, between 0.5% and 5% by weight of diolefins, between 20% and 50%by weight of mono-olefins, and between 10 ppm and 0.5% by weight ofsulphur, generally including less than 300 ppm of mercaptans. Themercaptans are generally concentrated in the light gasoline fractionsand more precisely in the fraction with a boiling point of less than120° C.

Treatment of the gasoline described in the present process principallyconsists of:

-   -   selectively hydrogenating the diolefins to mono-olefins;    -   transforming the light saturated sulphur-containing compounds,        principally mercaptans and light sulphides, into heavier        sulphides or mercaptans by reaction with the mono-olefins.

The hydrogenation of diolefins to mono-olefins is illustrated below bythe transformation of 1,3-pentadiene, which is an unstable compoundwhich easily polymerizes, into pent-2-ene by addition of hydrogen.However, secondary mono-olefin hydrogenation reactions must be limitedsince, as shown in the example below, they would result in the formationof n-pentane.

The sulphur-containing compounds which are to be transformed areprincipally mercaptans. The principal mercaptan transformation reactionconsists of thioetherification of mono-olefins by mercaptans. Thisreaction is illustrated below by the addition of propane-2-thiol topent-2-ene to form a propylpentylsulphide.

In the presence of hydrogen, sulphur-containing compound transformationmay also be carried out by the intermediate formation of H₂S which maythen add to unsaturated compounds present in the feed. However, this isa minor pathway under the preferred reaction conditions.

In addition to mercaptans, the compounds which may be transformed intoheavier compounds are sulphides and principally dimethylsulphide,methylethylsulphide and diethylsulphide, CS₂, COS, thiophane andmethylthiophane.

In certain cases, it is also possible to observe reactions fortransforming light nitrogen-containing compounds, principally nitrites,pyrrole and its derivatives, into heavier compounds.

The process described in the present invention consists of bringing thefeed to be treated, mixed with a stream of hydrogen, into contact with acatalyst containing at least one metal from group VIB (group 6 in thenew periodic table notation: Handbook of Chemistry and Physics, 76^(th)edition, 1995-1996) and at least one non-noble group VIII metal (groups8, 9 and 10 of said classification), deposited on a porous support.

In particular, it has been established that catalyst performance isimproved when the catalyst has the following characteristics:

The amount, by weight of the oxide, of the group VIB element in theoxide form is strictly more than 12% by weight and preferably strictlypore than 14%. The group VIB metal is preferably selected frommolybdenum and tungsten. More preferably, the group VIB metal ismolybdenum.

The catalyst also contains a non-noble group VIII metal, preferablyselected from nickel, cobalt and iron. More preferably, the non-noblegroup VIII metal is constituted by nickel. The amount of non-noble groupVIII metal, expressed in the oxide form, is less than 15% by weight andis preferably in the range 1% by weight to 10% by weight.

The mole ratio between the non-noble group VIII metal and the group VIBmetal is in the range 0.2 to 0.5 mol/mol and is preferably in the range0.25 to 0.45 mol/mol.

Preferably, a catalyst is used with a total pore volume, measured bymercury porosimetry, of more than 0.4 cm³/g, preferably in the range 0.4to 0.8 cm³/g and highly preferably in the range 0.5 to 0.7 cm³/g.Mercury porosimetry is carried out using the ASTM D4284-92 standard witha wetting angle of 140°, using an Autopore III model from Micromeritics.

The specific surface area of the catalyst is preferably less than 250m²/g, more preferably in the range 30 m²/g to 150 m²/g.

Further, the pore volume of the catalyst, measured by mercuryporosimetry, of pores with a diameter of more than 0.05 microns, is inthe range 10% to 40% of the total pore volume and is preferably in therange 15% to 35% of the total pore volume and more preferably in therange 18% to 35% of the total pore volume.

The volume of pores of the catalyst with a diameter of more than 0.1microns preferably represents at most 20% of the total pore volume andmore preferably at most 15% of the total pore volume. The inventors haveobserved that this pore distribution limits gum formation in thecatalyst.

The volume of pores of the catalyst with a diameter between 0.004 and0.009 microns represents preferably 1 to 5% of the total pore volume andmore preferably 2 to 4% of the total pore volume.

Preferably, the catalyst of the invention contains neither alkali metalsnor alkaline-earth metals.

Preferably, the catalyst of the invention does not contain any halogenand particularly any fluor.

Preferably, the catalyst of the invention under its oxide form andbefore catalytic test does not contain any carbon.

The catalyst support is preferably a porous metal oxide selected fromalumina, silica, silicon carbide and a mixture of those oxides. Morepreferably, alumina is used, still more preferably pure alumina.

Highly preferably, cubic gamma alumina or delta alumina is used; morepreferably, delta alumina is used.

Preferably, a support having a total pore volume, measured by mercuryporosimetry, in the range 0.4 to 0.9 cm³/g is used, preferably in therange 0.5 to 0.8 cm³/g.

Further, the pore volume of the support, measured by mercuryporosimetry, of pores with a diameter of more than 0.1 micron ispreferably in the range 0 to 30% of the total pore volume, morepreferably in the range 5% to 20% of the total pore volume.

The volume of pores of the support with a diameter of more than 0.05microns is in the range 10% to 50% of the total pore volume, preferablyin the range 15% to 40% of the total pore volume.

The specific surface area of the support is preferably less than 250m²/g, more preferably in the range 30 m²/g to 150 m²/g.

A preferred implementation of the invention corresponds to using acatalyst containing an amount of nickel oxide in the form of NiO in therange 1% to 10%, a molybdenum oxide content in the form of MoO₃ of morethan 12% and a nickel/molybdenum mole ratio in the range 0.25 to 0.45,the metals being deposited on a pure alumina support, the degree ofsulphurization of the metals constituting the catalyst being more than80% and the volume of pores of said catalyst with a diameter of morethan 0.05 microns being in the range 18% to 35%.

The catalyst of the invention may be prepared using any technique whichis known to the skilled person, in particular by impregnating elementsfrom groups VIII and VIB onto the selected support. Said impregnationmay, for example, be carried out using the technique known to theskilled person as dry impregnation, in which exactly the desiredquantity of elements is introduced in the form of salts which aresoluble in the selected solvent, for example demineralized water, tofill the porosity of the support as exactly as possible. The support,which is by then filled with solution, is preferably dried. Thepreferred support is alumina, which may be prepared from any type ofprecursor and shaping tools which are known to the skilled person.

After introducing the group VIII and VIB elements, and optionallyshaping the catalyst, it undergoes an activation treatment. Thistreatment generally aims to transform the molecular precursors of theelements into the oxide phase. In this case, it is an oxidizingtreatment, but simple drying of the catalyst may also be carried out. Inthe case of an oxidizing treatment, also termed calcining, this isgenerally carried out in air or in diluted oxygen, and the treatmenttemperature is generally in the range 200° C. to 550° C., preferably inthe range 300° C. to 500° C. Examples of salts of group VIB and VIIImetals which may be used in the catalyst preparation process are cobaltnitrate, nickel nitrate, ammonium heptamolybdate and ammoniummetatungstate. Any other salt which is known to the skilled person whichhas sufficient solubility and which can decompose during the activationtreatment may also be used.

After calcining, the metals deposited on the support are in the oxideform. In the case of nickel and molybdenum, the metals are principallyin the MoO₃ and NiO forms. Before contact with the feed to be treated,the catalysts undergo a sulphurization step. Sulphurization ispreferably carried out in a sulphoreducing medium, i.e. in the presenceof H₂S and hydrogen, to transform metal oxides into sulphides such asMoS₂ and Ni₃S₂, for example. Sulphurization is carried out by injectinga stream containing H₂S and hydrogen, or a sulphur-containing compoundwhich can decompose into H₂S in the presence of catalyst and hydrogen,over the catalyst. Polysulphides such as dimethyldisulphide are H₂Sprecursors which are routinely used to sulphurize catalysts. Thetemperature is adjusted so that the H₂S reacts with metal oxides to formmetal sulphides. Said sulphurization may be carried out in situ or exsitu (outside or inside the reactor) with respect to thehydrodesulphurization reactor at temperatures in the range 200° C. to600° C. and more preferably in the range 300° C. to 500° C.

In order to be active, the metals have to be substantially sulphurized.An element is considered to be “substantially” sulphurized when the moleratio between the sulphur (S) present on the catalyst and said elementis at least 60% of the theoretical mole ratio corresponding to totalsulphurization of the element under consideration:(S/element)_(catalyst)≧0.6×(S/element)_(theory)in which:

(S/element)_(catalyst) is the mole ratio between the sulphur (S) and theelement present on the catalyst;

(S/element)_(theory) is the mole ratio between the sulphur and theelement corresponding to total sulphurization of the element to thesulphide.

This theoretical mole ratio depends on the element under consideration:

-   -   (S/Fe)_(theory)=1    -   (S/Co)_(theory)=8/9    -   (S/Ni)_(theory)=2/3    -   (S/Mo)_(theory)=2/1    -   (S/W)_(theory)=2/1

If the catalyst comprises a plurality of metals, the mole ratio betweenthe S present on the catalyst and the assembled elements must also be atleast 60% of the theoretical mole ratio corresponding to totalsulphurization of each element to the sulphide, the calculation beingcarried out pro rata for the relative mole fractions of each element.

As an example, for a catalyst comprising molybdenum and nickel with arespective mole fraction of 0.7 and 0.3, the minimum mole ratio(S/Mo+Ni) is given by the relationship:(S/Mo+Ni)_(catalyst)=0.6×{(0.7×2)+(0.3×(2/3)}

Highly preferably, the degree of sulphurization of the metals is morethan 80%.

Sulphurization is carried out on metals in the oxide form withoutcarrying out a prior metal reduction step. Sulphurizing reduced metalsis known to be more difficult than sulphurizing metals in the oxideform.

In the selective hydrogenation process of the invention, the feed to betreated is mixed with hydrogen before being brought into contact withthe catalyst. The quantity of hydrogen which is injected is such thatthe mole ratio between the hydrogen and the diolefins to be hydrogenatedis more than 1 (stoichiometry) and less than 10, preferably in the range1 to 5 mol/mol. Too large an excess of hydrogen may cause too muchhydrogenation of mono-olefins and as a result, reduce the octane numberof the gasoline. The whole feed is generally injected into the reactorinlet. However, it may be advantageous in some cases to inject afraction or all of the feed between two consecutive catalytic bedsplaced in the reactor. This implementation can allow the reactor tocontinue operating if the inlet to the reactor is blocked with depositsof polymers, particles or gums present in the feed.

The mixture constituted by gasoline and hydrogen is brought into contactwith the catalyst at a temperature in the range 80° C. to 220° C.,preferably in the range 90° C. to 200° C., with a liquid hourly spacevelocity (LHSV) in the range 1 h⁻¹ to 10 h⁻¹. The pressure is adjustedso that the reaction mixture is mainly in the liquid form in thereactor. The pressure is in the range 0.5 MPa to 5 MPa and is preferablyin the range 1 to 4 MPa.

The gasoline treated under the conditions mentioned above has a reduceddiolefins and mercaptans content. Generally, the gasoline producedcontains less than 1% by weight of diolefins and preferably less than0.5% by weight of diolefins. The amount of light sulphur-containingcompounds with a boiling point less than that of thiophene (84° C.)which is generally converted is more than 50%. Thus, it is possible toseparate the light fraction of the gasoline by distillation and to sendsaid fraction directly to the gasoline pool without complementarytreatment. The light fraction of the gasoline generally has an end pointof less than 120° C., preferably less than 100° C. and more preferablyless than 80° C.

This novel catalyst is particularly suitable for use in the processdescribed in European patent EP-A-1 077 247.

EXAMPLE 1 Preparation of Catalysts A, B, C and D (Not in Accordance), Eand F (in Accordance with the Invention)

Catalysts A, B, C, D, E and F were prepared using the dry impregnationmethod. The synthesis protocol consisted of carrying out dryimpregnation of a solution of ammonium heptamolybdate and nickelnitrate, the volume of the aqueous solution containing the metalprecursors being equal to the water take-up volume corresponding to themass of the support to be impregnated (total volume of water which canpenetrate into the porosity). The concentrations of the precursors inthe solution were adjusted to deposit the desired amounts by weight ofmetal oxides on the support. The solid was then left to mature atambient temperature for 12 hours, and dried at 120° C. for 12 hours.Finally, the solid was calcined at 500° C. for two hours in air (1l/g.h). The alumina support used was an industrial support supplied byAxens. The characteristics of the prepared catalysts are shown in Table1 below. The prepared catalysts were distinguished by their active phasecontent.

TABLE 1 Characteristics of catalysts A, B, C, D, E, F, in the oxide formCatalyst A B C D E F Wt % of 5.2 8.1 10.0 11.2 12.1 14.1 MoO₃ Wt % of1.1 1.6 2.2 2.3 2.5 2.7 NiO Ni/Mo 0.4 0.38 0.43 0.40 0.40 0.37 moleratio S(BET), 120 115 112 108 106 102 m²/g Total pore 0.68 0.65 0.620.60 0.58 0.55 vol, cm³/g Hg pore 0.19 0.18 0.18 0.17 0.16 0.15 vol,cm³/g 28% 28% 29%  28%  28%  27% (pores > 0.05 microns) and as % oftotal pore vol Hg pore 0.02 0.2 0.02 0.01 0.01 0.01 vol, cm3/g  3%  3% 3% 1.6% 1.7% 1.8% (0.004 micron < pores < 0.009 micron) and as % oftotal pore vol

According to the porosity, specific surface area, amount of MoO₃ and theNi/Mo mole ratio criteria, catalysts E and F were thus in accordancewith the invention; in contrast, catalysts A, B, C and D (lowestmolybdenum contents) were not in accordance with the invention.

Evaluation of Catalysts

The activity of catalysts A, B, C, D, E and F was evaluated using a testfor selective hydrogenation of a mixture of model molecules carried outin a stirred 500 ml autoclave reactor. Typically, between 2 and 6 g ofcatalyst was sulphurized at atmospheric pressure in a sulphurizationunit in a mixture of H₂S/H₂ constituted by 15% by volume of H₂S at 1l/g.h of catalyst and at 400° C. for two hours (5° C./min ramp-up)followed by a constant temperature stage of 2 hours in pure hydrogen at200° C. This protocol produced degrees of sulphurization of more than80% for all of the catalysts of the invention. The sulphurized catalystwas transferred into the reactor, sealed from the air, then brought intocontact with 250 ml of model feed at a total pressure of 1.5 MPa and atemperature of 160° C. The pressure was kept constant during the test byadding hydrogen. The feed used for the activity test had the followingcomposition: 1000 ppm by weight of sulphur in the form of 3-methylthiophene, 100 ppm by weight of sulphur in the form of propane-2-thiol,10% by weight of olefin in the form of 1-hexene, in n-heptane.

The time t=0 of the test corresponded to bringing the catalyst and thefeed into contact. The test duration was fixed at 45 minutes and gaschromatographic analysis of the liquid effluent obtained allowed anevaluation of the activities of the various catalysts for thehydrogenation of isoprene (formation of methylbutenes), thehydrogenation of 1-hexene (formation of n-hexane) and transformation ofpropane-2-thiol into heavier compounds (disappearance ofpropane-2-thiol) to be carried out. The activity of the catalyst foreach reaction was defined with respect to the rate constant obtained foreach reaction, normalized to one gram of catalyst. The rate constant wascalculated by considering the reaction to be first order:A(X)=k(X)/min which: A(X)=activity of catalyst for reaction X, in min⁻¹/g ofcatalyst;

-   -   m=mass of catalyst (oxide form) used in test;    -   k=rate constant for the reaction under consideration, in min⁻¹,        calculated using the formula:        k(X)=(1/45)*1n(100/(100-conv(X)))

in which 45 =duration of test in minutes;

-   -   Conv(X) conversion of compound X; X=isoprene or propane-2-thiol        or 1-hexene;    -   X: reaction under consideration    -   X=isoprene: hydrogenation of isoprene    -   X=1-hexene: hydrogenation of 1-hexene    -   X=propane-2-thiol: conversion of propane-2-thiol.

The selectivity of the catalyst towards isoprene hydrogenation is equalto the ratio of the activities of the catalyst in the hydrogenation ofisoprene and 1-hexene: A(isoprene)/A(1-hexene).

The results obtained for the various catalysts are shown in Table 2below.

TABLE 2 Performances of catalysts in model molecule test Catalyst A B CD E F A(isoprene) * 10³ 2.4 3.4 3.6 4.5 4.7 4.9 A(1-hexene) * 0.0140.018 0.022 0.024 0.027 0.029 10³ A(isoprene)/ 171 189 163 187 174 169A(1-hexene) A(propane-2- 11.7 Infinite* Infinite* Infinite* Infinite*Infinite* thiol) * 10³ *complete conversion of propane-2-thiol.

It can be seen that all of the catalysts were highly selective asregards the diolefin hydrogenation reaction. These catalysts could thussubstantially hydrogenate isoprene without significantly hydrogenating1-hexene.

It can also be seen that under the test conditions, conversion of lightmercaptans was complete for all of the catalysts apart from catalyst A,which had less of the active phase.

In the case of catalysts B, C, D, E and F, an infinite activity meantcomplete conversion of propane-2-thiol.

In contrast, only catalysts E and F of the invention had a maximumisoprene hydrogenation activity.

It thus appears that the catalysts of the invention are capable ofsimultaneously carrying out selective hydrogenation of the diolefin withsimultaneous conversion of the light mercaptan.

EXAMPLE 2 Influence of Degree of Sulphurization

Catalyst E described above was evaluated in the model molecule testdescribed in Example 1 (identical feed and operating conditions) butwithout the prior sulphurization step. The degree of sulphurization ofthe solid was thus zero. The reduction in the temperature of theconstant temperature stage with the H₂S/H₂ mixture (from 400° C. totypically 100° to 150° C.) during the catalyst sulphurization protocolon the sulphurization bench could also produce intermediate degrees ofsulphurization for catalyst E. Table 3 records the catalytic resultsobtained on said catalyst as a function of its degree of sulphurization.It can be seen that prior sulphurization of the catalyst had a majorbeneficial effect on the activity of the catalyst in the hydrogenationof isoprene and in the conversion of propane-2-thiol, as well as on itsselectivity.

TABLE 3 Performance of catalyst E as a function of its degree ofsulphurization E, non sulphurized E, sulphurized Degree of 0 45 65 86sulphurization, % A(isoprene) * 10³ 0.3 2.4 3.3 4.7 A(1-hexene) * 10³0.010 0.014 0.019 0.027 A(isoprene)/ 18 71 173 174 A(1-hexene)A(propane-2- 3 Infinite* Infinite* Infinite* thiol) * 10³ *totalconversion of propane-2-thiol

EXAMPLE 3 Influence of Ni/Mo Mole Ratio

In this example, catalysts G and H were prepared using the operatingprotocol described in Example 1. These catalysts only differedsubstantially from catalyst E in their nickel contents, and thus in theNi/Mo mole ratio (Table 4). Thus, they were not in accordance with theinvention.

TABLE 4 Characteristics of catalysts G and H in the oxide form CatalystG H Wt % of 12.1 12.4 MoO₃ Wt % of 0.8 8.6 NiO Ni/Mo 0.13 1.34 moleratio S(BET), 106 100 m²/g Total pore 0.58 0.55 vol, cm³/g Hg pore 0.170.16 vol, cm³/g 29% 29% (pores > 0.05 microns) and as % of total porevolume

Catalysts G and H were evaluated in the model molecule test described inExample 1. For these catalysts, the sulphurization protocol which wasadopted could produce degrees of sulphurization of more than 80%. Thesecatalysts were compared with catalyst E, which had a Ni/Mo mole ratio of0.4, falling within the preferred range, and a similar degree ofsulphurization (Table 5).

TABLE 5 Performance of catalysts E, G and H in a model molecule testCatalyst E G H Degree of 86% 85% 89% sulphurization A(isoprene) * 10³4.7 1.3 5.0 A(1-hexene) * 10³ 0.027 0.010 0.030 A(isoprene)/ 174 130 167A(1-hexene) A(propane-2- Infinite* 10.2 Infinite* thiol) * 10³ *totalconversion of propane-2-thiol

It will be observed that catalyst G (Ni/Mo ratio of 0.13) had a lowerisoprene hydrogenation activity and propane-2-thiol conversion thancatalyst E of the invention. It will also be observed that the largeincrease in the nickel content (catalyst H, Ni/Mo ratio of 1.34) did notimprove the performance of the catalyst in terms of activity andselectivity.

EXAMPLE 4 Influence of Macropore Volume in the Range 10% to 40% of TotalPore Volume

Catalysts I, J and K were prepared using the protocol described inExample 1 using different alumina supports Al-1, Al-2 and Al-3 suppliedby Axens the properties of which are shown in Table 6 below.

TABLE 6 Properties of supports Al-1, Al-2, Al-3 Al-1 Al-2 Al-3 SBET(m²/g) 145    137    293    Total pore volume 0.73 1.10 0.75 (Hg) cm³/gPore volume (Hg) 0.09 0.32 0.01 pores > 0.1 micron, cm³/g V (0.1microns), % of 12% 29% 1% total pore volume Pore volume (Hg) 0.22 0.490.03 pores > 0.05 microns, cm³/g V (0.05 microns), % of 30% 45% 4% totalpore volume

The characteristics of these catalysts and that of catalyst E are shownin Table 7 below. Catalysts E and I were in accordance with theinvention. Catalyst J was not in accordance with the invention as thepore volume fraction of pores with a diameter of more than 0.05 micronswas greater than 40% (45%). Catalyst K was also not in accordance withthe invention as the pore volume fraction of pores with a diameter ofmore than 0.05 microns was less than 10% (3%).

TABLE 7 characteristics of catalysts E, I, J and K Catalyst E I J K Wt %of MoO₃ 12.1 12.0 12.3 12.1 Wt % of NiO 2.5 2.4 2.5 2.2 S(BET), m²/g 106120 116 278 Total pore 0.58 0.62 1.00 0.65 volume, cm³/g Pore volume0.16 0.21 0.45 0.02 (Hg), cm³/g (pores > 0.05 micron) Pore volume 0.080.09 0.31 0.01 (Hg), cm³/g pores > 0.1 micron) Pore volume 28% 34% 45%3% (pores > 0.05 micron), as % of total pore volume Pore volume 14% 15%31% 2% pores > 0.1 micron), as % of total pore volume SPD (g/cm³)* 0.690.65 0.48 0.59 *Settled packing density

The settled packing density (SPD) corresponds to the maximum quantity ofcatalyst in a given volume and is normalized to one gram of catalyst percubic centimeter. This was evaluated using a RETSCH AS 200 controlvibrator and a measuring cylinder of known volume and diameter adaptedto the granulometry of the products (the diameter of the measuringcylinder must be 10 times that of the particles). After calibration, themeasuring cylinder, with volume V, was filled with the test product onthe vibrator. Vibration was maintained for 3 minutes at an amplitude of0.03 inches, keeping the level constant by adding product. At the end ofsettling, the surface of the product was skimmed level with the upperpart of the sample and the mass of the full measuring cylinder wasweighed. The SPD was then obtained by dividing the mass, corrected forthe loss on ignition of the catalyst, by the volume of the measuringcylinder. In general, the lower the porosity of the catalyst, thegreater will be the charging density.

These catalysts were tested on a total catalytic cracking gasoline thecharacteristics of which are provided in Table 8 below. The conjugateddiolefins content was determined based on the reaction of conjugateddienes with maleic anhydride in accordance with the Diels-Alderreaction. The MAV (maleic anhydride value) was proportional to theamount of diolefin present and was determined using the standard IFPmethod: method 9407. The MAV was expressed in milligrams of maleicanhydride reacted per gram of sample. The IFP9407 method is similar tothe standardized 326-82UOP method which provides the DV (diene value),the two values being linked by the relationship MAV=3.86 DV. The amountof aromatics and mono-olefins in the feed and the effluent werequantified by chromatography. The light mercaptans of the feed andeffluent were quantified by chromatography. The equipment used was aHP5890 Series II (Agilent Technologies) chromatograph coupled to aspecific detector, a 355 (Sievers Inc., Boulder, Colo., USA). The columnused was a non-polar PONA (50 m, 0.2 mm, 0.20 microns) column. Theoperating conditions were derived from the ASTM D 5623 standard methodand the sulphur-containing compounds were identified by comparison withthe retention times for reference sulphur-containing compounds.

TABLE 8 Characteristics of total catalytically cracked gasoline Scontent 3460 ppm Light mercaptans*, S content  116 ppm MAV 17.5Aromatics content 36.5% by weight Mono-olefins content 34.4% by weightASTM distillation   5% point: 30° C.   95% point: 233° C. *methanethiol,ethanethiol and propanethiols

The following protocol was used to evaluate the catalysts on a realfeed. 50 cm³ of catalyst was sulphurized in a mixture of n-heptane +4%DMDS (dimethyldisulphide)/H₂, the H₂/sulphurization feed volume ratiobeing 500 normal liters/liter of feed (Nl/l) and the HSV of thesulphurization feed being 2 h⁻¹ (volume of sulphurization feed pervolume of catalyst per hour). The temperature ramp-up was 1° C./min to aconstant temperature stage of 350° C. The constant temperature stagelasted 4 hours. The temperature was then dropped to 120° C., thesulphurization feed was replaced with pure n-heptane for 4 hours, thenthe FCC gasoline was injected and the operating conditions were adjustedto the desired values. The test operating conditions were as follows:total pressure=2.5 MPa, H₂/feed ratio=6 Nl/l, HSV=3 h⁻¹. The catalystswere evaluated at 140° C. and at 160° C., the duration of each constanttemperature stage being adjusted as a function of the stabilizationperiod of the catalyst, evaluated by regular analyses of the MAV of theeffluent.

BRIEF DESCRIPTION OF DRAWINGS

The change in the residual MAV of the effluent as a function of time forthe 4 catalysts is shown in FIG. 1.

FIG. 1 shows that the catalysts E and I, in accordance with theinvention, eliminate diolefins most effectively at 140° C. and 160° C.since the residual MAV obtained is the lowest. Catalyst J, characterizedby too high a pore volume, had a substantial hydrogenating activitydeficit. The activity of catalyst K over the first 50 hours wascomparable with catalyst E and I, but it was less resistant to crushingand thus it deactivated more. Residual carbon analyses carried out onthe used catalysts after extracting with toluene showed that the carboncontent of catalyst K was about twice as high as the carbon content ofcatalyst E and I.

For the set of catalysts, under the selected operating conditions,mono-olefin hydrogenation remained marginal and below 2%.

TABLE 9 Conversion of light mercaptans at 140° C. and 160° C. obtainedwith catalysts E, I, J, K Conversion at 140° C. Conversion at 160° C.Catalyst E 94% 100% Catalyst I 93% 100% Catalyst J 89%  95% Catalyst K90%  96%

Table 9 shows the change in the conversion of light mercaptans for the 4catalysts at each temperature after catalyst stabilization (last part ofeach stage). It can be seen that under the selected operatingconditions, all of the catalysts converted the light mercaptans of thefeed to a large extent, said conversion being complete for catalysts Eand I at 160° C. In contrast, it can be seen that catalysts E and I,which were in accordance with the invention, were more effective thancatalysts J and K in eliminating light mercaptans.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forthuncorrected in degrees Celsius and, all parts and percentages are byweight, unless otherwise indicated.

The entire disclosures of all applications, patents and publications,cited herein and of corresponding French application No. 05/13.172,filed Dec. 22, 2005, is incorporated by reference herein.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A process comprising selectively hydrogenating a gasoline containingpolyunsaturated compounds and saturated light sulphur-containingcompounds, whereby the polyunsaturated compounds are hydrogenated intomonounsaturated compounds and whereby, jointly, the saturated lightsulphur-containing compounds are transformed into heavier compounds byreaction with the unsaturated compounds contained in the gasoline,wherein the reactions are conducted in contact with a catalystcomprising one or more metals from group VIB including at leastmolybdenum, and at least one non-noble metal from group VIII includingat least nickel, deposited on a porous catalyst support, in which: theamount, by weight of oxide, of the group VIB metal(s) is greater than12% by weight; the amount, by weight of oxide, of the group VIIImetal(s) is less than 15% by weight; the metals in said catalyst have adegree of sulphurization of at least 60%; the volume of pores with adiameter of more than 0.05 microns is in the range 10% to 40% of thetotal pore volume of the catalyst; and the mole ratio between the nickeland molybdenum, Ni/Mo, is in the range of 0.2 to 0.5 mol/mol.
 2. Aprocess according to claim 1, in which the catalyst comprises an amountof the oxide of the group VIII element in the range of 1% to 10% byweight.
 3. A process according to claim 1, in which the degree ofsulphurization of the metals in said catalyst is more than 80%.
 4. Aprocess according to claim 1, in which the Ni/Mo mole ratio is in therange of 0.25 to 0.45.
 5. A process according to claim 1, in which thecatalyst has a total pore volume of more than 0.4 cm³/g.
 6. A processaccording to claim 1, in which the catalyst has a total pore volume inthe range of 0.4 cm³/g to 0.8 cm³/g.
 7. A process according to claim 6,in which the catalyst support has a total pore volume in the range of0.5 cm³/g to 0.7 cm³/g.
 8. A process according to claim 1, in which thevolume of pores of the catalyst with a diameter of more than 0.1 micronsrepresents at most 20% of the total pore volume.
 9. A process accordingto claim 8, in which the volume of pores of the catalyst with a diameterof more than 0.1 micron represents at most 15% of the total pore volume.10. A process according to claim 1, in which the volume of pores of thecatalyst with a diameter of more than 0.05 micron represents 15% to 35%of the total pore volume.
 11. A process according to claim 10, in whichthe volume of pores of the catalyst with a diameter of more than 0.05micron represents 18% to 35% of the total pore volume.
 12. A processaccording to claim 1, in which the specific surface area of the catalystis less than 250 m²/g.
 13. A process according to claim 1, in which thecatalyst support is a porous metal oxide selected from alumina, silica,silicon carbide and a mixture of said oxides.
 14. A process according toclaim 13, in which the catalyst support is constituted by pure alumina.15. A process according to claim 13, in which the catalyst supportcomprises cubic gamma alumina or delta alumina.
 16. A process accordingto claim 15, in which the catalyst support comprises delta alumina. 17.A process according to claim 13, in which the catalyst support has apore volume in the range of 0.4 to 0.9 cm³/g.
 18. A process according toclaim 17, in which the catalyst support has a pore volume in the rangeof 0.5 to 0.8 cm³/g.
 19. A process according to claim 13, in which thevolume of pores of the support with a diameter of more than 0.1 micronrepresents 0 to 30% of the total pore volume.
 20. A process according toclaim 19, in which the volume of pores of the support with a diameter ofmore than 0.1 micron represents 5% to 20% of the total pore volume. 21.A process according to claim 13, in which the volume of pores of thesupport with a diameter of more than 0.05 microns represents 10% to 50%of the total pore volume.
 22. A process according to claim 21, in whichthe volume of pores of the support with a diameter of more than 0.05microns represents 15% to 40% of the total pore volume.
 23. A processaccording to claim 1, in which the gasoline is brought into contact withthe catalyst at a temperature in the range of 80° C. to 220° C. with aliquid hourly space velocity in the range of 1 h⁻¹ to 10 h⁻¹ and at apressure in the range of 0.5 to 5 MPa.
 24. A process according to claim1, wherein the specific area of catalyst support is 30-150 m²/g.